fix tests

For no discernible reason, when the GLA module from Catlab.jl was moved to this repo, an error was introduced into the test suite. The cause should be tracked down and fixed.

```
GLA: Test Failed at /Users/ksb/code/GraphicalLinearAlgebra/test/linear_algebra/GLA.jl:141
Expression: (f ⊕ g) * [x; y] == [f * x; g * y]
Evaluated: [0, 0, 28, 73, 118] == [1, 2, 28, 73, 118]
```